1. Field of the Invention
The present invention relates to a touch panel which is one kind of pointing device and, particularly, to a touch panel utilizing photoelasticity.
2. Prior Art
A touch panel is used as a pointing device for specifying a position on a display unit of a personal computer.
Touch panels of the resistance film type, electrostatic capacity type and optical type have already been put into practical use.
The touch panel of the resistance film type has a constitution in which two pieces of resistance film are arranged opposed to each other while maintaining a suitable gap, and a voltage is applied to one of the resistance films. This touch panel detects a depressed position by utilizing the fact that a voltage detected when the two pieces of resistance films come in contact varies depending upon the depressed position.
The touch panel of the electrostatic capacity type has a structure in which a pair of electrodes are arranged opposed to each other while maintaining a suitable gap, and a voltage is applied across the electrodes. This touch panel detects a depressed position by utilizing the fact that the electrostatic capacity across the electrodes varies depending upon the depressed position.
Various types of optical touch panels have been proposed. For example, a touch panel can have a structure in which the upper surface of the touch panel is scanned by two laser beams, and a depressed position is detected by detecting the angle of emission of the laser beam interrupted by the depressed position.
In the touch panel of the resistance film type, however, the resistance film has a transparency as low as 80 to 90%. When arranged on the surface of the display, therefore, a deterioration in the brightness of the display is not avoidable.
In the touch panel of the electrostatic capacity type, on the other hand, the detection sensitivity must be set to be low to prevent erroneous operation.
Further, the optical touch panel is affected by obstacles such as dust on the touch panel and its constitution is complex.
The present invention was accomplished in view of the above-mentioned circumstances, and has an object of providing a simply constituted touch panel which maintains a high transparency and a high sensitivity.
The touch panel according to a first invention comprises:
a homogeneous polymer sheet in the shape of a flat plate;
light sources arranged along two neighboring side walls of the polymer sheet;
transmitted light polarizing means arranged along the other side walls of the polymer sheet opposite the two side walls along which the light sources are arranged, to polarize light emitted from the light sources and passed through the polymer sheet;
transmitted light detecting means for detecting light polarized by the transmitted light polarizing means; and
depressed position specifying means for specifying the depressed position of the polymer sheet based upon the result detected by the transmitted light detecting means.
In the present invention, the angle of the polarized light incident through the polarizing sheet on the side wall of the polymer sheet is changed by the double-refraction when the polymer sheet is depressed, and the quantity of the light passing though another polarizing sheet on another side of the polymer sheet. By detecting a change of the transmitted light, it becomes possible to detect the depressed position.
The touch panel according to a second invention further has means for polarizing light from the light sources, that are arranged between the light sources and the polymer sheet to polarize light emitted from the light sources.
In the present invention, the angle of the polarized light incident through the polarizing sheet of the side surface of the polymer sheet is changed by the double-refraction when the polymer sheet is depressed. By further polarized light passing through the another polarizing sheet of the another side of the polymer sheet, it becomes possible to detect the depressed position by relying upon a change in the transmitted light.